Alternative Crosslinking Methods for Sodium Alginate Resulting in Hydrogels with Suitable Application Properties

abstract

English

Sodium alginate represents a pioneer gel-forming component in the field of materials engineering, known for its unique capabilities such as high biocompatibility, low toxicity, and especially its ability to form strong, flexible gel structures with excellent stability. This polymer was the focus of the present study, which deals with the preparation of alginate gels with the potential to influence their final application properties (transparency, syneresis, viscoelastic properties, etc.). Two strategies were selected leading to the gelation of sodium alginate, namely ionic cross-linking by the external gelation method (diffusion of calcium ions into the alginate sol) and ionic cross-linking by the internal gelation method (delayed gelation using limited soluble calcium salt and D-glucono-δ-lactone). Subsequently, optimization of the preparation of alginate gels was performed, their mechanical properties were characterized using selected rheometric tests (amplitude sweeps with shear deformation and time sweeps), and finally, the influence of several factors (polymer concentration, amount of cross-linking agent, gelation time, addition of sucrose, etc.) on the final properties of the prepared gels was investigated. It has been demonstrated that as the polymer concentration decreases, the mechanical strength of the gels also decreases, while, for example, the transparency of gels with lower polymer concentrations increases. The amount of cross-linking agent used plays an important role; with its addition, the degree of cross-linking increases, and consequently, the mechanical strength of the alginate gel also increases. The final properties of the hydrogels can also be influenced by the gelation rate, which affects, for example, their homogeneity (gels formed at a higher gelation rate tend to be less homogeneous). In the presented work, it was possible to slow down the gelation rate by adding phosphate ions, which led to higher homogeneity of the prepared gels but did not significantly affect their mechanical properties. A major issue in the preparation of hydrogel materials is also a phenomenon known as syneresis, which is generally undesirable. The present work demonstrated that, in some cases, this phenomenon can be slowed down by adding sucrose to the alginate sol before gelation. Another significant contribution of this work is the finding that, in ionic cross-linking of alginate by the external gelation method, not only the type of cation affects the final properties of the gels, which is a well-known fact, but in some cases, the type of anion used also influences the final properties of the gels. An interesting part of the work is also the optimization of the analysis of the mechanical properties of alginate gels through compression tests. During these tests, the sample is compressed in the rheometer between two planar sensors, and the normal force exerted by the sample on the upper plate of the rheometer is recorded. This is one of the most easily visualizable rheometric tests.

sodium alginate; polysaccharides; hydrogels; rheology; viscoelastic properties

KOUŘILOVÁ, L.; SMILEK, J.; KADLEC, M.

12. 9. 2024

FCH VUT

Brno

1

https://www.fch.vut.cz/chl/konference/program/bookofabstracts-pdf-p269547